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SubjectRe: Raise initial congestion window size / speedup slow start?
Ed W wrote:
>>> Does someone have some pointers on where to look to modify initial
>>> congestion window please?
>> Are you sure that's the issue? The backlog is in incoming, is it not?
> Well, I was simplifying a little bit, actually I have a bunch of
> protocols in use, http is one of them
>> Having dealt with moderately long delays push TB between timezones,
>> have you set your window size up? Set
>> /proc/sys/net/ipv4/tcp_adv_win_scale to 5 or 6 and see if that helps.
>> You may have to go into /proc/sys/net/core and crank up the rmem_*
>> settings, depending on your distribution.
>> This allows the server to push a lot of data without an ack, which is
>> what you want, the ack will be delayed by the long latency, so this
>> helps.
> I think I'm misunderstanding something fundamental here:
> - Surely the limited congestion window is what throttles me at
> connection initialisation time and this will not be affected by
> changing the params you mention above? For sure the sliding window
> will be relevant vs my bandwidth delay product once the tcp connection
> reaches steady state, but I'm mostly worried here about performance
> right at the creation of the connection?
> - Both you and Alan mention that the bulk of the traffic is "incoming"
> - this implies you think it's relevant? Obviously I'm missing
> something fundamental here because my understanding is that the
> congestion window shuts us down in both directions (at the start of
> the connection?)
> Thanks for the replies - I will take it over to netdev
Perhaps they will give you an answer you like better.

Bill Davidsen <>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein

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